Myelination of axons in the nervous system is critical for not only conduction of action potentials, but also for providing tropic support to ensure long term survival of neurons in both the central and peripheral nervous systems. Myelin disorders are a major cause of neurological disease, and can be caused by genetic disorders, infectious disease, and inflammation. Therefore, understanding the pathways that control gene expression patterns in myelinating cells is a critical step in not only elucidating developmental pathways, but also to provide insight into means by which remyelination after nerve injury can be accelerated. The genetic control of myelination has been a major focus of research, and critical transcription factors and their target gene networks have begun to be elucidated. Interestingly, recent studies have demonstrated that formation of myelin-and it longs term maintenance-depends upon not only gene activation, but also downregulation of genes that inhibit myelin formation. Although substantial progress has been made to identify gene expression changes that coordinate myelination, there have been relatively few studies examining the chromatin modifications required for myelination. For example, myelin maintenance depends upon a program of gene repression, but practically nothing is known regarding the role of histone/DNA methylation in this vital aspect of myelination. The long term objective of our laboratory is to elucidate an integrated mechanism of myelination based on critical genetic and epigenetic switches required for myelin formation and maintenance. Specifically, this proposal focuses on testing the involvement of the polycomb epigenetic pathway in peripheral nerve myelination. Chromatin immunoprecipitation analyses will be used to determine the developmental regulation of epigenetic markers in response to injury and aging. The analysis will focus on epigenetic changes that occur in gene loci that are repressed during the myelination process, and test for the first time the involvement of the polycomb pathway in formation and long term maintenance of myelin. Finally, this proposal also takes advantage of several unique aspects of peripheral nerve, which facilitate the epigenetic analysis that we have proposed here.